M. catarrhalis is an important human mucosal pathogen that contributes to otitis media in infants and exacerbates conditions such as chronic obstructive pulmonary disease in the elderly. In view of the increased incidence of M. catarrhalis infection and increased virulence and antibiotic resistance found in modern clinical isolates, there is a need to identify and develop new therapies targeting this pathogen. Currently, there is no M. catarrhalis vaccine approved for human use.
The lipooligosaccharides (LOS) of M. catarrhalis share a high degree of structural homology across the three known serotypes (A, B and C), including a common glucose core, indicating the potential for broad based coverage if an antibody response to a common epitope can be elicited.
The present invention provides a synthetically produced vaccine approach targeting the LOS cores of M. catarrhalis. Native M. catarrhalis LOSs are composed of branched oligosaccharides anchored to the cell membrane via a KDO2-lipid A linker. The KDO2-lipid A glycolipid motif is found in many species of gram negative bacteria (Edebrink et al., Carbohydr. Res., 295:127-146, 1996).
There is evidence that an antibody response to the LOS is a major part of the natural human immune response and that the anti-LOS antibodies from exposed patients are bactericidal to all the M. catarrhalis serotypes (U.S. Pat. No. 6,685,949). Monoclonal antibodies derived from animals exposed to killed M. catarrhalis are able to bind to all three serotype LOS structures equally well and display bactericidal activity towards all (Gergova et al., Curr. Microbiol., 54:85, 2007). These antibodies are thought to bind to an LOS core structure shared by all three serotypes. These results suggest that it should be possible to elicit an immunogenic response against all three serotypes using an antigen composed of the M. catarrhalis LOS core or derivative thereof.
LOS preparations isolated and purified from cellular material have been shown to be lethal to mice (Fomsgaard et al., Infect. Immun., 66:1891, 1998). The toxicity of the LOS preparations has been attributed to the KDO2-lipid A motif, more specifically the lipid A component. Id. Several groups have tried to remove the lipid A portion from the isolated molecules (Gu et al., Infect. Immun., 66:1891, 1998; Yu et al., Infect. Immun., 73:2790, 2005; Yu et al., Infect. Immun., 75:2974, 2007; U.S. Pat. No. 6,685,949). However, these methods do not completely and consistently remove the toxic lipid A portion.
The present invention provides synthetic M. catarrhalis LOS cores that are free of the KDO2-lipid A moiety and are homogenous. Such synthetic cores of M. catarrhalis LOS provide several benefits for vaccine development. The present invention allows for the production of homogenous antigen compositions at high purity and at robust levels without contaminating carbohydrate structures that are an almost inevitable consequence of isolation from biological mixtures.
These synthetic oligosaccharide cores may include a linker to conveniently facilitate formation of conjugate molecules. These synthetic oligosaccharide cores can be modified in ways not possible with isolates from natural sources, i.e., by systematically varying length and composition, by functionalizing side chains, and by controlling the antigen-protein carrier conjugation ratio, etc. This enables ready access to minor sequences, deletion sequences, and other variants on the natural structures that would be difficult or impossible to obtain from natural sources in high purity and sufficient quantity for conjugation.